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Final Vendetta: AES & MVS Version available for Pre-Order

Flain said:
Hopefully the cart behaves when it finally comes out, my last purchase of a new neogeo game was Vengeance Hunters, which works great but when you put it in a multislot it never gives up its attract mode. So once the neogeo cycles through to vengeance hunters it stays there forever. Brought it up on their discord and looks like they no longer have the guy with the neogeo coding skills to fix it (the cart has a sdcard slot for updates and all too so could be fixed, but they lack the people/staff to do it).

Crossed fingers for this cart, but not overly hopeful
Click to expand...

I don't want to distract the discussion too far from Final Vendetta, but this is interesting. I just began to look at Knight's Chance in the MAME debugger because it does the exact same thing. It just loops its own attract mode and never moves on to another slot.

I know basically nothing about coding and assembly, so it is entirely possible that I don't stand any chance of figuring out how to make it work, but I've looked at how Metal Slug runs through its own attract mode in the debugger too and the process seems to make sense to me. I've found some locations where it is reading or writing the bit that controls the system rom status.

Relevant part from the dev wiki:
https://wiki.neogeodev.org/index.php?title=BIOS_RAM_locations#System_Related

$10FD81BIOS_SYSRET_STATUSbyteBIOSInternal value which stores the function code that SYSTEM_RETURN will call.
  • 0 : Init bram/select valid game for eye-catcher
  • 1 : Set the EL-LED to the correct value
  • 2 : Switch to the next slot, relaunch eye-catcher
  • 3 : After a gameover, save the playtime for bookeeping, switch to DEMO mode, reset the workbackup ram
  • 4 : Switch next slot (select p1 pressed)
  • 5 : Switch to previous slot (select p2 pressed)
  • 6 : Called after a coin deposit, does nothing
 
Last edited:
lithy said:
I don't want to distract the discussion too far from Final Vendetta, but this is interesting. I just began to look at Knight's Chance in the MAME debugger because it does the exact same thing. It just loops its own attract mode and never moves on to another slot.

I know basically nothing about coding and assembly, so it is entirely possible that I don't stand any chance of figuring out how to make it work, but I've looked at how Metal Slug runs through its own attract mode in the debugger too and the process seems to make sense to me. I've found some locations where it is reading or writing the bit that controls the system rom status.

Relevant part from the dev wiki:
https://wiki.neogeodev.org/index.php?title=BIOS_RAM_locations#System_Related

$10FD81BIOS_SYSRET_STATUSbyteBIOSInternal value which stores the function code that SYSTEM_RETURN will call.
  • 0 : Init bram/select valid game for eye-catcher
  • 1 : Set the EL-LED to the correct value
  • 2 : Switch to the next slot, relaunch eye-catcher
  • 3 : After a gameover, save the playtime for bookeeping, switch to DEMO mode, reset the workbackup ram
  • 4 : Switch next slot (select p1 pressed)
  • 5 : Switch to previous slot (select p2 pressed)
  • 6 : Called after a coin deposit, does nothing
Click to expand...
We should maybe create another thread for this because it is an interesting topic! Was way too curious to not investigate this further (maybe for a reason :) ).

You are not wrong with the BIOS_SYSRET_STATUS value, although it does not seem to be the main cause of the issue with Metal Slug / Knights Chance.
What is happening with Metal Slug is that it calls the system_return BIOS function at the end of the attract mode, with a BIOS_SYSRET_STATUS set to 2 (this is set by the BIOS and not the game). The BIOS then checks for the next inserted slot, and if it finds one, it will change slot and ask the new game to start running the game from "DEMO" position (BIOS_USER_REQUEST = 2). If there is no more games inserted, it will just do the same thing but ignore the slot switching.

So what is up with knights chance? Well, if you set a breakpoint (you will find the address at 0xC00444) at the system_return function you would see that the game never calls this function, hence never returns the power to the BIOS to switch game. It loops in its own world and while it looks for the slot switching button, it does not honor the rolling slot switching feature.

Since knights chance is available for download, you could probably patch it by adding a jmp to system_return() at the end of the DEMO, but, it is a bit harder for games that only comes in cartridge form.
 
The latest news mentions a custom cartridge made by the Terraonion team to protect the data :) so no rom at all :)
 
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